The present invention relates to a wheel drive unit which is a combination of a wheel support rolling bearing unit, a constant velocity joint unit and a snap ring, and is used for rotatably supporting with respect to a suspension unit, a driven wheel {the front wheel of a FF vehicle (front engine, front drive wheel) the rear wheel of both a FR vehicle (front engine, rear drive wheel) and a RR vehicle (rear engine, rear drive wheel) and all wheels of a 4WD vehicle (four drive wheel)} supported on an independent suspension type suspension, and for rotationally driving the driven wheel.
In order to rotatably support a vehicle wheel with respect to a suspension unit, various kinds of rolling bearing units for wheel support with an outer ring and inner ring assembled so as to be freely rotatable via rolling elements, are used. Moreover, a wheel support rolling bearing unit for supporting a driven wheel in a suspension of the independent suspension type and rotationally driving the driven wheel, must be combined with a constant velocity joint to smoothly transmit (maintain constant velocity) the rotation of the drive shaft to the abovementioned vehicle wheel, regardless of the relative displacement between a differential gear and the driven wheel and of a steering angle applied to the wheel. FIG. 6 shows a typical bearing unit 3 for wheel drive wherein a rolling bearing unit 1 for wheel support and a constant velocity joint 2 are combined together for this kind of purpose.
This rolling bearing unit for wheel support 1 is formed by rotatably supporting a hub 5 and an inner ring 6 on the inner diameter side of an outer ring 4 via a plurality of rolling elements 7. Of these, the outer ring 4 when connectingly secured to a knuckle 9 (refer to FIG. 7 mentioned below) constituting a suspension unit by means of a first flange 8 provided on the outer peripheral face thereof, does not rotate even at the time of use. Furthermore, a double row of outer ring raceways 10 is provided on the inner peripheral face of the outer ring 4, and the hub 5 and the inner ring 6 are rotatably supported on the inner diameter side, concentric with the outer ring 4.
Of these, the hub 5 is provided with a second flange 11 for supporting the wheel, on a portion near an outer end (the end which is on the outside in a widthwise direction of the vehicle when fitted to the vehicle, namely, the left hand side of each figure including FIG. 6) of the outer peripheral face. Furthermore, the first inner ring raceway 12 is formed on a central portion of the outer peripheral face of the hub 5. Similarly, an inner ring 6 with a second inner ring raceway 14 formed on an outer peripheral face thereof, is externally secured to a small diameter step 13 formed on an inner end (the end which is on the middle side in a widthwise direction of the vehicle when fitted to the vehicle, namely the right hand side of each figure.). Moreover, in the center portion of the hub 5, a spline bore 15 is provided, so that the hub 5 is formed in a hollow cylindrical shape.
On the other hand, the constant velocity joint 2 has an outer ring 16 for constant velocity joint, an inner ring 17 for constant velocity joint and a spline shaft 18. Of these, the outer ring 16 for constant velocity joint and the spline shaft 18 constitute a drive member 19. That is, the spline shaft 18 is provided on an outer end of the drive member 19 and is freely engaged with the spline bore 15, and the outer ring 16 for constant velocity joint is provided on an inner end of the drive member 19. At a plurality of places on the inner peripheral face of the outer ring 16 for constant velocity joint around the circumferential direction are respectively formed outside engaging grooves 20 at right angles to the circumferential direction. Moreover, regarding the inner ring 17 for constant velocity joint, a second spline bore 21 is formed at right angles to the circumferential direction in a center portion, and on the outer peripheral face, inside engaging grooves 22 are formed at right angles to the circumferential direction in portions coinciding with the outside engaging grooves 20. Moreover, balls 23 are provided between each of the inside engaging grooves 22 and each of the outside engaging grooves 20 so as to be freely rotatable along each engaging groove 22 and 20, with the balls 23 being retained in a cage 24. At a part of the inner peripheral face of the outer ring 16 for constant velocity joint, portions between pairs of circumferentially adjacent outside engaging grooves 20 constitute cage guide faces 25. Each cage guide face 25 is positioned on a single spherical surface with a displacement center of the constant velocity joint 2 as the center thereof. Regarding the shape of the constituent elements of this kind of constant velocity joint 2, this is similar to the case of a well know Rzeppa type or Birfield type constant velocity joint, and since this has no relevance to the gist of the present invention, detailed description is omitted.
In combining the above described constant velocity joint 2 and the wheel support rolling bearing unit 1, the spline shaft 18 is inserted into the spline bore 15 of the hub 5 from the inner side towards the outer side. Then a nut 27 is screwed onto an external thread portion 26 provided on an outer end portion of the spline shaft 18 projecting from an outer end face of the hub 5, and then by tightening, these are connected and secured together. In this condition, since the inner end face of the inner ring 6 is abutted against the outer end face of the outer ring 16 for constant velocity joint, there is no displacement of the inner ring 6 in a direction to come off from the small diameter step portion 13. At the same time, an appropriate pre-load is applied to each of the rolling elements 7.
Moreover, when fitted to the suspension unit of a vehicle, a male spline portion 29 provided on an outer end of a drive shaft 28 is spline engaged with a second spline bore 21 provided in a central portion of the inner ring 17 for constant velocity joint. Then, a snap ring 37 which is stoppingly engaged in an engaging groove 30 formed around the whole periphery in the outer peripheral face at the outer end of the male spline portion 29, is engaged with an engaging step portion 32 formed in an opening rim at the outer end of the second spline bore 21, thereby preventing the male spline portion 29 from coming out from the second spline bore 21. Furthermore, the inner end of the drive shaft 28 is connectingly secured to the center of a trunnion 34 (refer to FIG. 1 showing a first example of an embodiment of the present invention) of a tripod type constant velocity joint 33 provided on an output shaft of a differential gear.
Regarding the first example of the abovementioned conventional construction shown in FIG. 6, the weight is increased because the rolling bearing unit 1 for wheel support and the constant velocity joint 2 are connectingly secured based on the threaded and tightened engagement between the male thread portion 29 and the nut 27. That is, providing the external thread portion 26 on the spline shaft 18 of the constant velocity joint 2 requires lengthening of the spline shaft 18, and the nut 27 also becomes necessary. Therefore the axial dimension and the weight of the bearing unit 3 for wheel drive are increased by the male thread portion 26 and the nut 27.
To address this problem, in the specification of U.S. Pat. No. 4,881,842 is disclosed as shown in FIG. 7, a bearing unit 3a for wheel drive that enables shortening of the axial dimension and a reduction in weight, by connectingly securing the rolling bearing unit for wheel support and the constant velocity joint by a relatively simple construction. Also in the case of the second example of the conventional construction shown in FIG. 7, a hub 5 is rotatably supported on the inside of an outer ring 4 secured to a knuckle 9, by rolling elements 7 arranged in a double row. Moreover, a spline shaft 18 of a drive member 19a is spline engaged with a spline bore 15 formed in a central portion of the hub 5. An engaging portion 35 is formed in an outer end surface of the spline shaft 18 for engaging with a tool for drawing the spline shaft 18 into the spline bore 15.
Furthermore, the spline shaft 18 is prevented from coming off from the hub 5 by a snap ring 31 which is stoppingly engaged in an engaging groove 36 formed in an outer peripheral face of the spline shaft 18 at a portion close to its tip end (outer end). In this condition, resilient ring 60 is resiliently compressed between the hub 5 and the outer ring 16 for constant velocity joint of the drive member 19a, thereby effecting play prevention of the spline shaft 18 and the hub 5. In the case of the second example of this kind of conventional construction, to the extent that connection of the rolling bearing unit 1a for wheel support and the constant velocity joint 2a is performed by the snap ring 31, an overall smaller size and lighter weight for the bearing unit 3a for wheel drive is achieved.
Moreover, in Japanese Patent Publication No. Tokukai Hei 10-264605 disclosed a bearing unit 3b for wheel drive such as shown in FIG. 8. A rolling bearing unit 1b for wheel support constituting the bearing unit 3b for wheel drive has a hollow hub 5a such that a constant velocity joint outer ring 16a constituting a constant velocity joint 2b corresponding to the drive member described in the claims, is connected to an inner end of the hollow hub 5a via a spacer 38. Of the inner and outer peripheral surfaces of this spacer 38 formed in a short cylindrical shape, an inner diameter side female spline portion 39 is formed on the inner peripheral surface of the spacer 38, and an outer diameter side male spline portion 40 corresponding to the first spline portion described in the claims is formed on the outer peripheral surface of the spacer 38. This spacer 38 is assembled on an outer peripheral face at the inner end of the hub 5a, with an inner diameter side male spline portion 41 formed on an outer peripheral surface thereof in spline engagement without play with the inner diameter side female spline portion 39. Then, in this condition, an inner end face of the spacer 38 is clamped by a crimped portion 42 formed on the inner end of the hub 5a, so that the spacer 38 is secured without play to the inner end of the hub 5a. Moreover, in Japanese Patent Publication No. Tokukai Hei 10-264605 is also disclosed a construction where the inner ring and the spacer are formed as one body.
On the other hand, an outer diameter side female spline portion 43 corresponding to the second spline portion described in the claims, which is formed on the inner peripheral face at the outer end of the outer ring 16a for constant velocity joint is spline engaged with an outer diameter side male spline portion 40. That is, the outer diameter side female spline portion 43 is formed in an inner peripheral face at the outer end of the outer ring 16a for constant velocity joint. Moreover, as mentioned above, the outer diameter side female spline portion 43 is spline engaged with the outer diameter side male spline portion 40 formed on the outer peripheral surface of the spacer 38.
A snap ring 31a spans between the outer diameter side female spline portion 43 and the outer diameter side male spline portion 40 which are spline engaged with each other as described above, so that the outer ring 16a for constant velocity joint cannot separate from the spacer 38. That is, the snap ring 31a is formed in a semi-circle annular shape and made to span between an inside engaging groove 44 corresponding to a first connecting portion, which is formed around the whole periphery in the outer peripheral surface of the spacer 38, and an outside engaging groove 45 corresponding to a second connecting portion described in the claims, which is formed around the whole periphery in the inner peripheral surface at the outer end of the outer ring 16a for constant velocity joint. Hence the outer ring 16a for constant velocity joint and the spacer 38 cannot be displaced from each other in the axial direction.
The construction of the connecting portion of the hub 5a and the outer ring 16a for constant velocity joint is as mentioned above, and this hub 5a is rotatably supported on the inner diameter side of the outer ring 4 by a double row angular type ball bearing. An inner ring 6 constituting this ball bearing is clampingly secured between an outer end face of the spacer 38 and a step face 46 existing on the outer end of a small diameter step portion 13 formed on an outer peripheral face at the central portion of the hub 5a. 
In the case of the bearing unit 3b for wheel drive described in Japanese Patent Publication No. Tokukai Hei 10-264605 as described above, the spline shaft 18 can be omitted from the second example of the conventional construction shown in FIG. 7, and to that extent, the cost and weight can be further reduced.
In the case of the second and third examples of the conventional construction shown in FIG. 7 and FIG. 8, in comparison to the case of the first example of the conventional construction shown in FIG. 6, a reduction of cost and weight is effected. However, in order to sufficiently maintain the durability of each constituent element, it is necessary to optimize the properties of each constituent element. That is, at the time of using the wheel drive unit, various kinds of stress such as, force in the compression direction, force of the bending direction, and force in the tension direction and the like, are applied to each constituent element of the rolling bearing unit for wheel support and the constant velocity joint which are combined together to form the wheel drive unit. However with regards to this point, heretofore no consideration has been given to make the properties of each constituent element optimum to deal with these stresses.
The present invention was invented taking this situation into consideration, in order to optimize the properties of each constituent element so as to ensure durability of the wheel drive unit.
The present invention provides a wheel drive unit comprising a rolling bearing unit for vehicle wheel, a constant velocity joint unit and a snap ring. The constant velocity joint unit comprises a first constant velocity joint having an output portion and a input portion connected to an output portion of a differential gear. A transmission shaft having an output end and an input end is connected to the output portion of the first constant velocity joint A second constant velocity joint having an output portion and an input portion is connected to the output end of the transmission shaft. The rolling bearing unit for vehicle wheel comprises an outer ring having an inner peripheral surface formed with outer ring raceways and being not rotatable during use, a hollow hub having an outer peripheral surface formed with an flange for supporting a vehicle wheel near the outer end thereof, with a first inner ring raceway at the middle portion thereof, and with a small diameter stepped portion formed near the inner end thereof. An inner ring having an outer peripheral surface is formed with a second inner ring raceway and fitted onto the small diameter stepped portion of the hub, the hub having the inner end plastically deformed radially outward to form a crimped portion to prevent the inner ring from coming out of the smaller diameter portion. A plurality of rolling members are rotatably provided between each of the outer ring raceways and the first and second inner ring raceways, and a first spline portion is provided on a peripheral surface portion of the hub or a member securely connected to the hub.
The second constant velocity joint comprises a drive member having a peripheral surface at the outer end thereof formed with a second spline portion in spline engagement relation with the first spline portion, and an outer ring for constant velocity joint at the inner end thereof to constitute the second constant velocity joint. A first engagement portion is provided on a peripheral surface portion of the hub or a member securely connected to the hub. A second engagement portion is provided on the peripheral surface at the outer end of the drive member. The snap ring spans between the first engagement portion and the second engagement portion to prevent disengagement between the first spline section and the smaller diameter stepped portion of the hub has a stepped face portion at the innermost end thereof. The inner ring has an inner end face abutted to the stepped surface portion. On the outer peripheral surface of the hub, at least the first inner ring raceway and the stepped surface portion is quench-hardened, while on the inner peripheral surface of the hub, at least a portion located on the inner diameter side of the quench-hardened stepped surface portion; and the crimped portion is not quench-hardened. At least one of the hub or the member securely connected to the hub and the drive member has a peripheral portion formed with an engagement groove for the first and second engagement portions and not quench-hardened. The outer ring for constant velocity joint is formed with outside engagement groove portions on the inner peripheral surface thereof with cage guide portions each existing between a circumferentially adjacent pair of the cage guide portions, and on the inner peripheral surface of the outer ring for constant velocity joint, at least the outside engagement groove portions and the cage guide portions is quench-hardened.
The wheel drive unit of the present invention comprises a rolling bearing unit for wheel support, a constant velocity joint unit and a snap ring.
Of these, the constant velocity joint unit has a first constant velocity joint for connecting an input portion thereof to an output portion of a differential gear, a transmission shaft with an input side end portion thereof connected to an output portion of the first constant velocity joint, and a second constant velocity joint with an input portion thereof to an output side end portion of the transmission shaft connected.
Furthermore, the rolling bearing unit for wheel support has an outer ring, a hollow hub, rolling elements and a first spline portion.
Of these, the outer ring has a double row of outer ring raceways on an inner peripheral face thereof and does not rotate at the time of use.
Moreover, the hub is provided with a flange for supporting a vehicle wheel, on a part near an outer end of an outer peripheral face thereof, and a first inner ring raceway on a central portion thereof. An inner ring with a second inner ring raceway formed on an outer peripheral face thereof is externally secured to a small diameter step portion formed on a part of the outer peripheral face near the inner end thereof, and the coming off of the inner ring from the small diameter step portion is prevented by a crimped portion formed by plastic deformation of the inner end portion in a radially outward direction.
Furthermore, the rolling elements are respectively provided severally so as to be freely rotatable between each of the outer ring raceways and each of the first and second inner ring raceways.
Moreover, the first spline portion is provided on the hub or on a part of a peripheral face of a member connectingly secured to the hub.
In addition, the second constant velocity joint incorporates a drive member with a second spline portion for spline engagement with the first spine portion provided on an outer end peripheral face thereof, and an inner end portion serving as a constant velocity joint outer ring constituting the second constant velocity joint.
Moreover, in a condition with the first spline portion and the second spline portion spline connected to each other, the snap ring spans between a first engaging portion provided on the hub or a part of the periphery of a member connectingly secured to the hub, and a second engaging portion provided on a peripheral face at the outer end of the drive member, thereby preventing the separation of the connection between the first spline portion and the second spline portion.
Furthermore, of the outer peripheral face of the hub, at least the first inner ring raceway portion and the stepped face portion existing at the innermost end of the small diameter step portion which abuts with the outer end face of the inner ring, are quench-hardened. Furthermore, at least a portion of the inner peripheral face of the hub, positioned on the inner diameter side of the portion that is quench-hardened corresponding to the small diameter step portion, and the portion for forming the crimped portion are not quench-hardened. Moreover, at least one portion of the peripheral face of at least one of the hub or a member connectingly secured to the hub, and the drive mentor, which is formed with the engaging groove for serving as the first connecting portion or the second connecting portion, is not quench-hardened. In addition, of the inner peripheral face of the outer ring for constant velocity joint, at least the outside engaging groove portion and the cage guide face portion existing between each of the circumferentially adjacent outside engaging groove pairs are quench-hardened.
According to the wheel drive unit of the present invention constructed as described above, because the properties of each constituent element can be such as to correspond optimally to the stress etc. applied to each member, the durability can be sufficiently ensured.
Firstly, of the outer peripheral face of the hub, because the first inner ring raceway portion is quench-hardened, the rolling fatigue life of this first inner ring raceway portion is improved. Furthermore, because the stepped face portion existing at the innermost end of the small diameter step portion is quench-hardened, the thrust load which this stepped face portion bears can be made sufficiently large. Accordingly, when the crimped portion is formed on the inner end portion of the hub in a condition with the outer end face of the inner ring abutted against the stepped face portion, so that the inner ring is secured to the hub, there is no plastic deformation of the stepped face portion. As a result, by clamping the inner ring with the crimped portion an appropriate pre-load can be applied to each rolling element.
Furthermore, at least a part of the inner peripheral face of the hub, positioned on the inner diameter side of the quench-hardened portion corresponding to the small diameter step portion, is not quench-hardened, and therefore there is no quench-hardened portion penetrating from the inner peripheral face of the hub to the outer peripheral face thereof. Therefore, the existence of a partially brittle portion in the hub is prevented. Hence damage such as cracking occurring in the hub during the process of quench-hardening of the hub, or lowering of the shock resistance of the hub can be prevented.
Furthermore, because the portion of the hub to be crimped is not quench-hardened, when forming the crimped portion in order to connectingly secure the inner ring to the hub, damage such as cracking does not occur at this crimped portion, and a high quality crimped portion can thus be formed. Furthermore, at one portion of the peripheral face of at least one of the hub or a member connectingly secured to the hub, and the drive member, which is formed with the engaging groove being the first connecting portion or the second connecting portion, is not quench-hardened. Therefore, damage such as cracking due to heat treatment does not occur in the portion where the abovementioned engaging groove is formed and where distortion can easily occur with heat treatment.
Moreover, of the inner peripheral face of the outer ring for constant velocity joint, the rolling fatigue life of the outer engaging groove portion is improved with the quench-hardening of the outer engaging groove portion. Furthermore, of the inner peripheral face of the outer ring for constant velocity joint, since the cage guide face portion existing between the circumferentially adjacent outer engaging groove pairs is quench-hardened, the wear resistance and seizure resistance of the cage guide face portion which rubbingly contacts with the outer peripheral face of the cage constituting the constant velocity joint can be improved.